How does the Enrich EIP (Content Enricher) work in Camel (enrich vs pollEnrich)?

The Content Enricher augments a message with data fetched from an external resource. Camel provides two variants:

• enrich(uri): Calls the external resource using a producer (e.g., HTTP GET, SQL query) and merges the response into the original message using an AggregationStrategy. The original Exchange is enriched in-place.
• pollEnrich(uri): Polls a consumer endpoint (e.g., file: or jms:) to fetch a resource and merges it. Useful for fetching reference data from a file or a JMS queue.

// enrich: HTTP GET to add product details to an order:
from("jms:queue:orders")
    .enrich("http://product-service/api/products",
            new AggregationStrategy() {
                public Exchange aggregate(Exchange orig, Exchange resource) {
                    String product = resource.getIn().getBody(String.class);
                    orig.getIn().setHeader("productDetails", product);
                    return orig;
                }
            })
    .to("direct:process");

// pollEnrich: fetch the latest reference file:
from("direct:start")
    .pollEnrich("file:/data/config?fileName=rates.csv", 3000,
                new FileBodyMergeStrategy())
    .to("direct:applyRates");

The key difference: enrich() PUSHES to the resource endpoint (producer call, needs active request); pollEnrich() PULLS from the resource endpoint (consumer poll). If pollEnrich() times out before finding data (timeout in ms, or -1 to wait indefinitely), it returns the original Exchange unchanged.

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